1. Field of the Invention
The present invention relates to a process for producing solar cells, and is directed particularly to a method for the formation of an anti-reflection coating on a silicon substrate having a p-n junction therein.
2. Description of the Prior Art
The conversion efficiency of solar cells is enhanced by covering the light receiving surface of the substrate with an anti-reflection coating to prevent the surface reflection of incident light. This anti-reflection coating is a metal oxide film having a thickness of .lambda./4 n (.lambda.: wavelength of incident light; n: refractive index of metal oxide film), formed on the front face of the substrate. The metal oxide film is formed, for example, by (a) vacuum deposition, (b) sputtering, (c) chemical vapor deposition, or (d) coating and baking of metal complex. Of these methods, (a), (b), and (c) are inferior in productivity because a vacuum system is used for the film formation, and all the methods (a) through (d) require, after formation of an anti-reflection coating on the entire area of the light receiving side of the substrate, local removal of the film by etching, and formation of a collector contact on the stripped area.
To eliminate these drawbacks, there has been proposed a process which comprises coating a p-n junction containing silicon substrate with a metal complex, printing a silver conductive paste on predetermined positions, of the coating, and heat-treating the resulting substrate to complete an anti-reflection coating and a silver contact at the same time, thus achieving the contact of the silver with the silicon substrate (IEEE Photovoltaic Specialists Conference, p.p. 360-361 (1976)).
However, it has been found that the produced solar cells according to this process show high contact resistance between the silver and the silicon substrate and are unsatisfactory in fill factor and conversion efficiency.